1. Field of the Disclosure
The present disclosure generally relates to nuclear medicine, and more particularly to apparatus and methods for attaching a drive system and a stand to a ring of a medicine gantry in a particular nuclear gantry.
2. Description of the Background Art
Nuclear medicine is a unique medical specialty wherein radiation is used to acquire images that show the function and anatomy of organs, bones or tissues of the body. Radiopharmaceuticals may be introduced into the body, either by injection or ingestion, and are attracted to specific organs, bones or tissues of interest. Such radiopharmaceuticals produce gamma photon emissions which emanate from the body. One or more detector heads are used to detect the emitted gamma photons, and the information collected from the detector head(s) is processed to calculate the position of origin of the emitted photon from the source (i.e., the body organ or tissue under study). The accumulation of a large number of emitted gamma positions allows an image of the organ or tissue under study to be displayed.
There are basically two types of imaging techniques, namely, positron emission tomography (PET) and single photon emission computed tomography (SPECT). Both PET and SPECT require gamma ray detector head(s) that calculate and store both the position of the detected gamma ray and its energy. Typically, detector head(s) include a scintillation plate which converts each received radiation event (e.g., the emitted gamma photons) into a scintillation or flash of light. An array of photomultiplier tubes positioned behind the scintillation plate and associated circuitry determine a coordinate location and a value of energy for each scintillation event. Generally, the detector head(s) is attached to a ring, and a drive system is mounted to a portion of the medicine gantry to rotate the ring.
In a nuclear medicine camera, there are several ways to mount the drive system. One way of mounting the drive system to the gantry is to mount the drive system to the stand to achieve proper tooth alignment (pinion gear centerline is parallel to ring centerline). Here, the stand often has a costly machined surface where the drive system mounts. Even after this surface is machined, the tolerance accumulation between this mounting surface on the stand and gear teeth on the ring may still be large. Furthermore, as the ring and stand both experience unequal deflections under load, the tooth alignment may vary. If the machined surface on the base frame is eliminated for cost reduction purposes, the tolerance accumulation and potential tooth misalignment may further increase.
Adjustable tooth clearance is often used between the pinion gear and ring in a nuclear medicine camera and is accomplished in various ways. One common way is to provide slotted mounting holes in the drive system's mounting plate. During assembly, the mounting plate is slid towards the ring until the desired tooth clearance is achieved bolts are then tightened to secure the connection. Depending on the direction of the slots, the assembler may need to lift some or all of the weight of the drive system to slide it into proper alignment. Additionally, when the drive system is removed, the adjustment procedure must be performed again if the drive system has to be reinstalled, thus resulting in additional process variation.
The ring and stand are generally fastened together at several points to adequately support the heavy loads of the detectors and other system components and also to minimize deflection under these loads. Due to tolerance accumulations and possible slight non-coplanarity of multiple mounting surfaces on the stand, the ring may be rigidly bolted into an overconstrained condition, causing binding of the ring as the ring rotates. If the number of attachment points is reduced, or if some or all of the joints are allowed to be non-rigid, the possibility of binding during rotation of the ring may be eliminated, but the system may also experience more deflection under load.
An apparatus and method of attaching the drive system to the ring with relative ease, accuracy and repetition is lacking in the field. Further, an apparatus and method of attaching the stand of a medicine gantry to its ring while allowing for tolerance and deflection is also lacking.